This application is based on application No. JP2000-298429 filed in Japan, the contents of which is hereby incorporated by reference.
1. Field of the Invention
The present invention relates to an improved driving apparatus and method that drives a driven member, such as a disk-like rotor that rotates or a slider that moves in a linear fashion. Specifically, it relates to an improved driving apparatus and method using electromechanical conversion elements, and more particularly to a truss-type improved driving apparatus and method using electromechanical conversion elements.
2. Description of the Related Art
Actuators are known in the conventional art that have a construction in which a drive unit comprising displacement members consisting piezoelectric elements, etc. is placed in pressure contact with a driven member using a pressure unit, wherein the bases of the displacement members are fixed to a fixing unit, and a synthesizing member is attached to the other ends thereof such that the displacement members cross each other.
A method to drive such an actuator such that the synthesizing member draws an elliptical locus has been proposed (Japanese Laid-Open Patent Application Sho 58-148682).
However, in this proposed method, because information regarding the locus of the synthesizing member is not detected for the adjustment of the locus, it is difficult to maintain the locus of the synthesizing member in such a way that the desired driving characteristics are obtained.
The present invention was created in view of this situation, and an object thereof is to provide an improved driving apparatus and method. Specifically, an object of the present invention is to provide an improved truss-type driving apparatus and method using electromechanical conversion elements, and more particularly, to provide a truss-type actuator that can detect information regarding the elliptical locus of the synthesizing member for the adjustment of the locus in order to ensure the desired driving characteristics, as well as to provide a driving method for such an actuator.
In order to attain this and other objects, according to one aspect of the present invention, the driving apparatus has (i) a base, (ii) multiple displacement members, the base ends of which are fixed to the base and the tip ends of which are combined at one location, said displacement members generating a prescribed displacement, (iii) a pressure unit that keeps the synthesizing member, at which the tip ends of the displacement members are combined, in pressure contact with the driven member, which comprises the object of driving, (iv) a driving circuit that impresses drive signals to the displacement members, (v) a controller that controls the driving circuit so that the synthesizing member moves in an elliptical path and the drive force is transmitted to the driven member, and (vi) a first detector that detects the amplitudes of the displacement members and the phase difference therebetween, wherein based on the results of detection by the detectors, the amplitudes or phases of the voltages impressed to the displacement members are changed to adjust the elliptical locus of the synthesizing member. In addition, the controller changes the phases of the impressed voltages to adjust the flatness of the elliptical locus. Furthermore, the controller changes the amplitudes and phases of the impressed voltages to adjust the direction of the elliptical locus. Moreover, the controller changes the amplitudes and phases of the impressed voltages to adjust the drive force transmitted to the driven member.
In this driving apparatus, the desired driving characteristics are obtained through detection of the amplitude and phase of each displacement member pertaining to the elliptical locus of the synthesizing member and adjustment of this locus based on the results of detection.
According to another aspect of the present invention, the driving apparatus further has a memory means that stores the target amplitudes and target phase differences that correspond to the target elliptical locus of the synthesizing member, and the controller changes at least either the amplitudes or phases of the impressed voltages so that the difference between the amplitudes detected by the first detector and the target amplitudes stored in the memory means and the difference between the phase difference detected by the first detector and the target phase difference stored in the memory means are eliminated. The memory means stores multiple target amplitudes and phase differences that correspond to the target elliptical locus of the synthesizing member in such a manner that they are associated with a timing at which the parameters of the elliptical movement should be changed, and the elliptical movement when the driven member begins to move is different from such movement at other times. Specifically, the elliptical movement is changed such that the driving characteristics include low speed and high torque when the driven member begins to move, while including high speed and low torque otherwise. Furthermore, according to another aspect, the controller drives only one of the multiple displacement members.
According to this aspect, because the controller changes either the amplitudes or phases of the impressed voltage such that the difference between the amplitudes detected by the first detector and the target amplitudes stored in the memory means and the difference between the phase difference detected by the first detector and the target phase difference stored in the memory means are eliminated, the elliptical locus of the synthesizing member is automatically adjusted and the desired driving characteristics are obtained. Furthermore, according to this aspect, if the target amplitudes and phase differences for the target elliptical locus, for the beginning of which low speed and high torque is used, whereas high speed and low torque is used otherwise, are stored in the memory means in such a way that they are associated with the timing at which the elliptical movement of the synthesizing member should be changed, smooth driving from the start of the elliptical movement through regular driving can be enabled.
According to another aspect of the present invention, the driving apparatus further has a second phase difference detecting means that detects the phase difference between the voltage impressed to each displacement member and the electric current drawn thereto, and the controller changes the drive frequency of each displacement member based on the phase difference detected by the second phase difference detecting means. After adjusting the driving frequencies to become the resonance frequencies based on the phase difference detected by the second phase difference detecting means, the controller changes either the amplitudes or phase of the impressed voltage such that the difference between the amplitudes and phase difference detected by the first detector and the target amplitudes and phase difference stored in the memory means, respectively, are eliminated. The multiple displacement members comprise multi-layer piezoelectric elements, and the first detecting means detects the amplitude and phase of the voltage impressed to each displacement member based on the electric current that is drawn to the multi-layer piezoelectric element.
According to this aspect, it is possible to reduce the phase difference between the voltage impressed to each displacement member and the current drawn thereto to zero or near zero by having the controller change the oscillation frequency of the oscillator based on the phase difference detected by the second phase difference detecting means, and consequently, each displacement member may be driven using an efficient resonance frequency. In addition, because the amplitudes and phase difference may be detected by the multi-layer piezoelectric elements themselves, which are incorporated in the driving apparatus as an actuator, the need for separate distortion sensors, etc. may be eliminated.